Power generator shut-off valve

ABSTRACT

A power generator has a hydrogen producing fuel and a fuel cell having a proton exchange membrane separating the hydrogen producing fuel from ambient. A valve is disposed between the fuel cell and ambient such that water is controllably prevented from entering or leaving the fuel cell by actuation of the valve. In one embodiment, multiple fuel cells are arranged in a circle around the fuel, and the valve is a rotatable ring shaped gate valve having multiple openings corresponding to the fuel cells.

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/698,457, filed Jul. 12, 2005, and U.S.Provisional Patent Application Ser. No. 60/757,823, filed Jan. 10, 2006.

BACKGROUND

In some fuel cell based power generators, hydrogen is extracted from afuel in the presence of water and then is introduced into a fuel cell toproduce electricity. In such generators, hydrogen may leak to ambienteven when power is not being drawn from the power generator. As hydrogenis lost, water migrates back to the fuel to replace the water consumedby the reaction that produced the hydrogen. If this process continues,energy may be slowly drained from a power generator, reducing the totalenergy available from the power generator for useful power generation.

Many such power hydrogen fuel based generators are thought to involvecomplex fuel processing, and require components which occupy significantvolume. Such power generators may be limited to comparatively large,high power applications. There is currently a need in the art forlighter weight and smaller sized power sources for applications such asportable electronic devices, wireless sensors, battlefield applications,and unmanned air vehicles. Such power sources should have a relativelylong shelf life when not in use. It is desirable to increase the energycapacity of current power sources so as to decrease power supplyreplacement intervals and/or increase operating life, while alsoreducing the size and weight of the power source.

SUMMARY

A power generator has a hydrogen producing fuel and a fuel cell having aproton exchange membrane separating the hydrogen producing fuel fromambient. A valve is disposed between the fuel cell and ambient such thatwater is controllably prevented from entering the fuel cell by actuationof the valve. In one embodiment, multiple fuel cells are arranged in acircle around the fuel, and the valve is a rotatable ring shaped gatevalve having multiple openings corresponding to the fuel cells.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional schematic representation of a powergenerator having a shutoff valve according to an example embodiment.

FIG. 2 is a cross-sectional schematic representation of an alternativepower generator having a shutoff valve according to an exampleembodiment.

FIG. 3A is a cross-sectional schematic representation of a corner of thepower generator illustrated in FIG. 1 according to an exampleembodiment.

FIG. 3B is a cross-sectional schematic representation of a corner of thepower generator illustrated in FIG. 2 according to an exampleembodiment.

FIG. 4 is a schematic representation of a fuel cell having a shutoffvalve according to an example embodiment.

FIG. 5 is a plot of power output versus time for a power generatoraccording to an example embodiment.

FIG. 6 is a schematic representation of an inlet from the power cell toambient illustrating the position of a shutoff valve according to anexample embodiment.

FIG. 7 is a partial cross sectional view of a cylindrical powergenerator incorporating a plurality of fuel cells according to anexample embodiment.

FIG. 8 is a cross sectional view of an alternative power generatorhaving a shut off valve.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanyingdrawings that form a part hereof, and in which is shown by way ofillustration specific embodiments which may be practiced. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention, and it is to be understood thatother embodiments may be utilized and that structural, logical andelectrical changes may be made without departing from the scope of thepresent invention. The following description is, therefore, not to betaken in a limited sense, and the scope of the present invention isdefined by the appended claims.

An electrical power generator is provided which generates hydrogen gasinternally through the reaction of water vapor with a moistureabsorbing, solid fuel substance, which hydrogen gas is reacted withatmospheric oxygen from the air at a fuel cell to generate electricalenergy. The reaction of hydrogen and oxygen also produces watermolecules as a byproduct at the fuel cell. This generated water ispassively diffused from the fuel cell as water vapor to a fuel chamberthat contains the solid fuel substance, where it reacts with the fuelsubstance to generate hydrogen gas. The electrical energy generated maybe used to power large or small devices that are connected to the powergenerator, depending on the size of the power generator. The powergenerator of the invention is particularly useful for powering miniaturedevices such as wireless sensors, cellular phones or other hand heldelectronic devices that are electrically connected to the anode andcathode of the one or more fuel cells of the power generator.

FIGS. 1 and 2 illustrate cross-sectional views of alternate powergenerator apparatuses for carrying out the process of the invention. Asseen in FIG. 1 and FIG. 2, an electrical power generator 10 comprises ahousing 36, at least one fuel cell 14 mounted within the housing 36, atleast one fuel chamber 12 for storing a fuel substance 44 mounted withthe housing 36, and a cavity 24 within the housing 36 extending from theat least one fuel cell 14 to the fuel chamber 12. Cavity 24 admits aflow of hydrogen gas from the fuel chamber 12 to the fuel cell 14, andadmits a flow of water vapor from the fuel cell 14 to the fuel chamber12. Fuel cell 14 generates electricity and fuel cell water from thereaction of hydrogen gas and oxygen gas from the air. Atmospheric oxygenenters into the housing 36 through at least one air inlet 20. The oxygengas then travels to the fuel cell 14 where it reacts with hydrogen gas,generating electricity and water molecules. The type of fuel cell isreferred to as a Proton Exchange Membrane (PEM) fuel cell, also known asa Polymer Electrolyte Membrane fuel cell.

In one embodiment, each air inlet 20 is formed in a shape that issuitable for inclusion of a shutoff valve 21. As such, the air inlets 20may be rectangular or circular in shape, consistent with requirement ofmating with the shutoff valve 21. The shutoff valve is also shown inFIGS. 2, 3A, and 3B. Further detail of the shutoff valve is shown at 600in FIG. 6. The shutoff valve 21 may be operated to shutoff the fuel cellfrom all ambient water, effectively shutting down the fuel cell andstopping it from producing electricity and using up its fuel when not inuse. The valve may be manually operated, or otherwise controlled asdesired. In one embodiment, each air inlet 20 is formed with the shutoffvalve, which may also be used to controllable limit the flow of ambientwater to the fuel in further embodiments, as well as to shut off suchflow completely.

As seen in FIG. 4, a typical PEM fuel cell comprises an electrolyticmembrane 42 positioned between a positive electrode, or cathode 16, onone side of the membrane, and a negative electrode, or anode 18, on theother side of the membrane. In typical hydrogen-oxygen PEM fuel cellbehavior, a hydrogen fuel (e.g. hydrogen gas) is channeled through flowfield plates to the anode, while oxygen is channeled to the cathode ofthe fuel cell. At the anode, the hydrogen is split into positivehydrogen ions (protons) and negatively charged electrons. Theelectrolytic membrane allows only the positively charged ions to passthrough it to the cathode. The negatively charged electrons must insteadtravel along an external circuit to the cathode, creating an electricalcurrent. At the cathode, the electrons and positively charged hydrogenions combine with oxygen to form water molecules.

Inside the generator, on the anode 18 side of the fuel cell, an initialflush of hydrogen or nitrogen gas is provided to remove residual oxygenfrom within the power generator. The purpose of this hydrogen ornitrogen flush is to remove residual oxygen from the anode of the powergenerator, thereby preventing a potentially explosive mixture ofhydrogen and oxygen from developing inside the power generator, where itcould easily be ignited by the catalyst on the fuel cell anode.Alternately, the generator may be initiated by the permeation of watermolecules from the humidity of the atmosphere outside the powergenerator, through the air inlet 20, and into the power generator. It isalso possible to add an initial amount of non-fuel cell water to thegenerator, in an amount substantially less than the amount of fuel cellwater generated by the fuel cell, to react with the fuel substance 44and initiate hydrogen gas generation. Such start-up water may be addedto the generator, for example, through an opening in the fuel chamber12, such as entry 46, or through another suitable means, such as throughair inlet 20. However, the process and apparatus of the invention aredesigned to operate without an externally provided water supply, i.e.the system is water-less except for water that is generated by the fuelcell and water molecules present in the atmosphere outside of the powergenerator. There is no incorporated or connected water supply, such as awater chamber or water reservoir, to provide water for reaction with thehydrogen fuel substance. The result of which is a significantimprovement in the energy density and specific energy of the powergenerator compared to conventional systems. Accordingly, the presentinvention provides a continuous, self-regulating process since thehydrogen-oxygen reaction produces exactly the required watercorresponding to the electrical power generated, wherein stoichiometricamounts of recycled water and solid fuel are used.

The process may be passive, running without actively controlled valvesor pumps. More particularly, once water is formed as a by-product of theoxygen-hydrogen reaction at the fuel cell 14, the produced waterpassively diffuses back through the fuel cell 14, into the cavity 24 andto the fuel chamber 12. This passive diffusion is enabled in part due toone or more water retention zones 22, in part due to the low humidityinside the cavity 24, as well as the construction of the fuel cellstack. Water retention zone 22 is highlighted by FIGS. 3A and 3B whichoffer corner views of the power generators illustrated in FIGS. 1 and 2.As used herein, and as shown in FIGS. 3A and 3B, a water retention zone22 comprises the channel extending from the air inlet 20 to each thefuel cell cathode 16. A water retention zone 22 is present at each fuelcell 14 which generates fuel cell water. Due to the geometry of thewater retention zone 22, diffusive water loss of fuel cell generatedwater molecules out of the air inlet is deterred, thereby maintaining ahigh concentration of water vapor at the fuel cell cathode 16. Insteadof losing water molecules to the ambient air, water retention zone 22causes generated water molecules to accumulate at the cathode 16,creating a region of high humidity between the cathode 16 and air inlet20. This molar flow rate can be described with more specificity via theequation below:

$J_{A} = \frac{D_{AB}*( {P_{A\; 1} - P_{A\; 2}} )}{R*T*( {Z_{2} - Z_{1}} )}$The transport of water vapor from the cathode 16 to the ambient air, andthe transport of oxygen from the ambient air to the cathode 16 are bothdiffusion controlled processes. The molar flux, or molar flow rate, of Ais J_(A), where A is the desired species, i.e. either water or oxygen.The molar flux of water or oxygen is a function of the diffusivityD_(AB), the partial pressure difference between point 1 and point 2(P_(A1)-P_(A2)), the gas constant R, the temperature T in Kelvin, andthe distance between points 1 and 2 (Z₂-Z₁). Additionally, flux isdefined as per area, with units of

$\frac{{kg}\mspace{11mu} A}{m^{2}\mspace{14mu}\sec}\mspace{11mu}{( {{{kilograms}\mspace{14mu}{of}\mspace{14mu} A},\;{{per}\mspace{14mu} m^{2}\mspace{11mu}{second}}} ).}$

The diffusion coefficient is the proportionality constant between theflux of a species to its concentration gradient. The diffusioncoefficient D_(AB) refers to the diffusion coefficient of species A inspecies B. In the present case, it refers to the diffusion coefficientof water vapor in air, or the diffusion coefficient of oxygen in air. Alarge diffusion coefficient will yield a large flux value, and a smalldiffusion coefficient will yield a small flux value. The diffusioncoefficient for oxygen in air is about 0.21 cm²/sec at room temperatureand normal room humidity, while the diffusion coefficient for watervapor in air at room temperature and humidity is about 0.24 cm²/sec.

Partial pressure is the fraction of the total pressure of a mixture ofgases that is due to one component of the mixture. A large partialpressure difference will generate a relatively large flux of thespecies, while a small partial pressure difference will generate arelatively small flux. The water retention zone is designed to give asmall partial pressure difference, e.g. about 10% to about 20% ofatmospheric oxygen partial pressure, to obtain the oxygen flux requiredfor the desired power level.

The gas constant is a product of Boltzmann's constant and Avogadro'snumber. The temperature in Kelvin affects the flux of the species ofinterest. Higher temperatures tend to reduce flux, while lowertemperatures tend to increase flux. Thus, the diffusion of gases, and byextension, their partial pressure differences, can be controlled byadjusting the channel geometry.

The power generators as seen in FIGS. 1 and 2 are designed to allowenough oxygen to diffuse from the ambient air, through the air inlet 20and to the cathode 16 with only a small pressure drop, e.g. 10% to 20%of the atmospheric oxygen pressure. The power generator may have highhydrogen permeation losses and thus reduced lifetime if operated at highpressures.

The chemical reaction that converts hydrogen and oxygen to water(2H₂+O₂→2H₂0) creates two moles of water for every mole of oxygen itconsumes. Further, the diffusivity of water vapor in air and thediffusivity of oxygen in air are similar. Accordingly, the partialpressure difference of water vapor must be roughly twice that of oxygento maintain equilibrium. Therefore, the power generator of the inventionhaving the above proportions maintains a humidified environment insteadof losing the generated water molecules to the atmosphere outside thegenerator.

Within the cavity 24, on the anode 18 side of the fuel cell 14, acomparatively low humidity region exists due to the moisture absorbing,hygroscopic nature of the fuel substance 44. Accordingly, the watergeneration and retention at the cathode 16 generates a moistureconcentration gradient and a gas pressure differential which causeswater molecules to diffuse back through the fuel cell 14, into thecavity 24 and to the fuel chamber 12 in the form of water vapor. Thiswater vapor then reacts with fuel substance 44, generating hydrogen gas.The generated hydrogen gas will then pass through cavity 24 and to thefuel cell anode 18 where it will react with oxygen to once againgenerate water molecules. This cycle may optionally continue until allof the fuel substance 44 is consumed.

During operation of the power generator, more generated water vapor willdiffuse back into the cavity than is lost out of the air inlet.Furthermore, fuel cell output is directly dependent on the flow ofoxygen and hydrogen reactants to the fuel cells, and hence the flow ofwater vapor to the fuel chamber. Accordingly, fuel cell output isproportional to the ratio of the area of the water retention zone to itslength. In an embodiment of the invention, the ratio of zone area tozone length per unit of power is from about 0.01 cm/mW to about 0.05cm/mW of power output for a single fuel cell in one embodiment. Ifmultiple fuel cells are incorporated, this ratio of zone area to zonelength per unit of power is divided by the number of fuel cells whichshare the reactants.

The generator will operate at reduced power if the geometry of the waterretention zone 22 is too restrictive to allow sufficient oxygen todiffuse to the fuel cells 14. Particularly, at a zone area to lengthratio of greater than 0.05 cm² area/1 cm length, excess water vapor willdiffuse out of the air inlet, and at a zone area to length ratio of lessthan 0.01 cm² area/1 cm length, not enough oxygen will reach the fuelcells to operate at a high efficiency. The same is true for the geometryof the cavity within the housing extending from the fuel cell to thefuel chamber, which admits a flow of hydrogen gas from the fuel chamberto the fuel cell, and which admits a flow of water vapor from the fuelcell to the fuel chamber.

In another embodiment, the power generator 10 may further include atleast one valve 26 for regulating the flow hydrogen gas from the fuelchamber 12 to the fuel cell 14, and for regulating the passage of watervapor from the fuel cell 14 to the fuel chamber 12. As shown in FIGS. 1and 2, valve 26 is positioned within the cavity 24 between fuel chamber12 and the fuel cell 14. In an embodiment of the invention, valve 26comprises a pneumatic valve that is controlled by gas pressure withinsaid cavity 24, pneumatically adjusting the conductance of water vaporto the fuel chamber 12. In one embodiment, valve 26 comprises apneumatically actuated flexible diaphragm 30 having a periphery that maybe fixed to the power generator housing 36 at a support 50; a valve disc28 positioned opposite the diaphragm 30; and a rod connector joins thevalve disc 28 and diaphragm 30. The valve 26 is in a closed positionwhen the valve disc 28 is in contact with a seal 38, preventing watervapor from reaching the fuel chamber 12. Alternately, the valve is in anopen position when the valve disc is separated from seal 38, allowingwater vapor to reach the fuel chamber 12 and allowing generated hydrogengas to reach the fuel cells 14. Seal 38 may comprise a portion ofhousing 36. Support 50 also may comprise part of housing 36. As seen inFIGS. 1 and 2, the fuel cell or fuel cells 14 may also be mounted insidethe housing by support 50.

The dimensions of the component parts of the valve may be very small inscale but may vary with respect to the particular application of thevalve. The diaphragm thickness and diameter should be within a certainrange depending on the desired power output. In one embodiment of theinvention, the diaphragm 30 comprises a thin circular plate having adiameter of from about 1 cm to about 3 cm, or from about 1 cm to about 2cm. The valve disc 28 may have a diameter of from about 0.2 to about 1cm, or may be from about 0.2 cm to about 0.5 cm. In one embodiment ofthe invention, the rod connector may comprise a screw or a bolt, but anyother means of connecting the diaphragm 30 to the valve disc 28 issuitable such that the valve can alternate between the open and closedpositions.

The actuation of the valve may be controlled by the internal gaspressure exerted on the diaphragm 30. As the internal gas pressure ofthe apparatus rises due to the generation of hydrogen gas, the diaphragm30 will bend or push outward slightly. This causes the connector to pullthe valve disc 28 against the seal 38, closing the valve and preventingthe flow of additional water vapor to the fuel chamber 12. With thevalve closed, hydrogen production ceases. This also prevents theinternal gas pressure from rising further. As hydrogen is consumed, suchas by fuel cells 14, the internal gas pressure drops, allowing the valvedisc 28 to disengage the seal 38 and opening the valve. Accordingly,hydrogen gas is automatically produced at the rate at which it isconsumed.

In one embodiment of the invention, the power generator 10 operates bymaintaining a fixed pressure, via the pneumatic valve 26. The powergenerator 10 should be able to operate down to low ambient pressures atreduced power output, and up to theoretically unlimited ambientpressures at full power output. In an embodiment of the invention, theinternal H₂ pressure of the apparatus when in the closed position isfrom about 0 kPa to about 1000 kPa. The valve will be fully shut when nohydrogen gas is used by the fuel cell, and will open the amount requiredto meet consumption rate of the hydrogen gas. In one embodiment of theinvention, the internal pressure of the power generator is maintained atabout 100 kPa at all times, wherein when the pressure drops below about10 kPa, the valve will open slightly until the internal pressure raisesto at or above about 500 kPa, causing the valve to close. Operatingpressures may be from about 0.5 atm (about 50 kPa) to about 2 atm (about202 kPa) for small scale applications such as portable electronicdevices or wireless sensors.

In general, the power generator 10 operates by maintaining a fixedpressure, usually a few psi over ambient, using the pneumatic valve 26.In one embodiment, generator 10 is able to operate down to low ambientpressures at reduced power output, and up to theoretically unlimitedambient pressures at full power output.

The power generator 10 may be maintained at an operating temperature offrom about −40° C. to about 85° C., or in a further embodiment, fromabout −20° C. to about 50° C., or from about 0° C. to about 50° C. orfrom about 20° C. to about 50° C. while in use.

For the purposes of this invention, the term “water vapor” does notinclude steam. While “water vapor” and “steam” are both forms of water,each has very different properties and uses. For example, a locomotivecan be driven by steam, but will not operate on the water vapor presentin humid air, as does the present invention. In and of itself, “watervapor” is the gas of individual water molecules that may form naturallyover a body of water at any temperature, including ice, or that may benaturally present in ambient air. It has a low partial pressure, so itcontains relatively few water molecules unless the water that forms itis heated. On the other hand, “steam” is made up of tiny hot waterdroplets produced by heating water to boiling. Steam contains about 100×more water molecules than does water vapor at 15° C., naturally expandswith high force and velocity, and large amounts of water can be boiledand transported off as steam. Water vapor is present in everyday air andcontains a much smaller number of water molecules than steam or liquidwater, and moves very slowly by natural diffusion. Only very smallamounts of water can be transported in the form of water vapor. Toillustrate, a single drop of water takes typically one hour to evaporateat room temperature, while an entire kettle of water can be boiled intosteam in about twenty minutes. Further, a steam powered generator wouldrequire a water supply or water source from which steam may begenerated. In contrast, the present invention provides an improvementupon the related art by eliminating such a water source. Accordingly,the apparatus and process of the present invention are designed tofunction at low operating temperatures using water vapor, not at highoperation temperatures using steam.

As seen in FIGS. 1 and 2, the power generator 10 may further include arestriction 32 united with the air inlet 20, regulating the diffusion ofatmospheric oxygen and atmospheric water molecules into the powergenerator. This restriction also aids in raising the humidity at thefuel cell cathode 16 due to impedance presented to outward diffusion ofwater vapor produced at the cathode 16. This increased humidity improvesthe operation of the fuel cell. The restriction comprises a hydrophobicmembrane that is substantially permeable to atmospheric oxygen gas, butsubstantially impermeable to water vapor, which membrane substantiallyobstructs the flow of fuel cell water into the atmosphere. Suitablematerials for this oxygen permeable, water vapor impermeable membranehaving the desired properties include fluoropolymer containing materialssuch as fluorinated ethylene propylene (FEP), perfluoroalkoxy, andnon-fluoropolymer containing materials such as oriented polypropylene(OPP), low density polyethylene (LDPE), high density polyethylene (HDPE)and cyclic olefin copolymers (COCs). One oxygen permeable, water vaporimpermeable membrane material comprises fluorinated ethylene propylene.In addition, for some embodiments, the membrane alone may not allowsufficient oxygen permeation to the cathode. Accordingly, a smallopening 48 (see FIG. 2) in the restriction 32 may be provided to allowthe ingress of extra atmospheric oxygen and atmospheric water moleculesinto the cavity to diffuse to the fuel cell cathode or cathodes.However, this opening may also cause some of the water vapor to diffuseout of the power generator 10. The required opening size is a functionof the power level, the diffusion path length, and the desired partialpressure drop. The size of this opening is very small in size and maycomprise from about 0.001% to about 1% of the entire surface area of themembrane.

The substantially non-fluid substance within the fuel chamber 12 maycomprise a material in powder, granule or pellet form and may be analkali metal, calcium hydride, lithium hydride, lithium aluminumhydride, lithium borohydride, sodium borohydride and combinationsthereof. Suitable alkali metals non-exclusively include lithium, sodiumand potassium. One material for the non-fluid substance is lithiumaluminum hydride. The fuel substance may be a solid, porous materialthat allows for the diffusion of gases and vapors. Further, thenon-fluid substance may also be combined with a hydrogen generationcatalyst to catalyze the reaction of the water vapor and the non-fluidsubstance. Suitable catalysts include non-exclusively include cobalt,nickel, ruthenium, magnesium and alloys and combinations thereof.

As seen in FIGS. 1 and 2, fuel chamber 12 may be bordered by porousvapor membrane 34. This membrane 34, attached to the housing 36 andjuxtaposed with the fuel chamber 12, is necessarily permeable to watervapor, so as to allow water vapor to pass into the fuel chamber 12 andreact with the solid fuel substance, thereby generating hydrogen gas. Itis also necessarily permeable to hydrogen gas, so as to allow generatedhydrogen gas to pass into the cavity 24 and back to the fuel cell 14.Suitable materials for this vapor membrane 34 having such dualproperties non-exclusively include porous polymers includingfluoropolymers, including expanded-polytetrafluoroethylene (ePTFE)laminates such as expanded Teflon®. Example ePTFE laminates areGORE-TEX® manufactured by W. L. Gore & Associates, Inc. of Delaware, andeVENT®, manufactured by BHA technologies of Delaware.

Referring to FIG. 2, in particular, is a cross-sectional schematicrepresentation of an alternate power generator of the invention havingan air inlet with a larger surface area compared to the generator ofFIG. 1. Similarly, in this embodiment, a hydrophobic membrane 32 that issubstantially permeable to atmospheric oxygen gas, but substantiallyimpermeable to water vapor, may be placed at air inlet 20. However, inorder to allow for the intake of water molecules from natural airhumidity in the atmosphere, a small opening 48 (e.g. about 0.008 cm²)opening may be cut into the membrane 32. This opening 48 will also allowextra oxygen to diffuse to the fuel cell cathodes. In an embodiment ofthe invention, the power generators of the invention will perform bestwhen in an environment having a relative humidity of at least about 5%,wherein the performance will improve with increasing humidity.

The embodiment of FIG. 2 may includes a pneumatic valve 26 which mayinclude a mesh diaphragm 30 and a water permeable, hydrogen impermeablemembrane 40 in juxtaposition with the mesh diaphragm 30 of the valve 26.The mesh diaphragm 30 may be permeable to water vapor and may be formedfrom a polymeric material, such as polyethylene terephthalate or a metalsuch as stainless steel. Suitable water permeable materials for thiswater permeable membrane 40 include perfluorinated polymers such asperfluorosulfonate ionomers. Also suitable are epoxides and chloroprenerubber. The water permeable membrane may comprise a perfluorosulfonateionomer membrane commercially available under the trademark Nafion® fromEI DuPont de Nemours & Co. of Delaware. Nafion® may be used in oneembodiment because it has a fluorinated backbone that makes it verystable, with sulfonic acid side chains to support high ionicconductivity. The water permeable, hydrogen impermeable membrane 40allows the diffusion of water vapor to the fuel chamber 12 withoutpassing the water vapor through the electrolytic membrane 42. Itprovides a large area path for water vapor to permeate into the fuelchamber and may allow the fuel cells 14 to operate at higher currentdensities than if the water is recovered solely though the fuel cellsthemselves. A similar material forms the electrolytic membrane 42 of theat least one fuel cell 14.

Accordingly, as can from FIG. 2, this power generator 10 provides dualavenues for the transport of fuel cell generated water molecules fromthe fuel cell cathode 16 to the fuel chamber 12. Specifically, in theembodiment of FIG. 2, the reaction of hydrogen gas and atmosphericoxygen in the fuel cell 14 results in the generation of fuel cell waterat the fuel cell cathode 16, and thereby generates electricity. Thisgenerated fuel cell water is retained in the water retention zone 22 andmay re-enter cavity 24 by either diffusing back through the fuel cell14, or by diffusing from the water retention zone 22 and permeatingthrough the mesh diaphragm 30 and water permeable membrane 40.

FIG. 5 offers an example of the power output vs. time plot for asmall-scale, micro-power generator of the invention. A micro-powergenerator of the invention may produce a power output of from about 1micro Watt to about 100 milli Watts, or from about 1 micro Watt to about1000 milli Watts, and energy densities of from about 0.1 W-hr/cc toabout 10 W-hr/cc in various embodiments. Larger power generators of theinvention may produce power output levels of from about 0.1 W to about100 W and energy densities of from about 0.1 W-hr/cc to about 10W-hr/cc.

FIG. 6 illustrates an example fuel cell 600 with a valve 605 in achannel or opening 607 that may be used between fuel 610 and ambient 615to prevent water from ambient from reaching the fuel when the fuel cellis not in use. In one embodiment, the valve 605 is positioned in anopening leading between ambient and a PEM membrane 620. The valve may bemanually operated, or may be closed using power from the fuel cell. Suchvalve could be operated automatically with an electrostatic, pneumatic,piezoelectric, or magenetic (solenoid) actuator. In one embodiment, thevalve is a gate valve. In further embodiments, the valve may be a globevalue, gate valve, butterfly valve, ball valve, or other type of valve.

Fuel cell 600 does not need to include the regulating values illustratedin prior embodiments. It may be a simple fuel cell with hydrogenproducing fuel 610, and a PEM membrane 620 that is exposed to ambient615 on one side and hydrogen produced by the fuel 610.

In further embodiments, the shutoff valve 605 comprises a diaphragm thatmay be moved electrostatically between an open and closed position. Inyet a further embodiment, it may be threaded member that mates withcorresponding threads in the opening 607. To open the valve, thethreaded member is unscrewed. To close the valve, the threaded membermay be screwed back in place. In one embodiment, the valve provides ahermetic seal when closed.

Illustrated in FIG. 7 is a partial cross sectional view of a cylindricalpower generator 10 of the invention having a plurality of fuel cells. Asseen in FIG. 7, in one embodiment, a plurality of fuel cells 14 arepositioned around a circumference of the power generator 10. The numberof fuel cells 14 may be varied, such as 5 as shown, or 8. Fewer or morefuel cells 14 may be used. A power generator 10 of the invention mayalso include an entry 46, through which fuel substance 44 may optionallybe replenished. Alternately, when fuel substance 44 is consumed, thepower generator may be disposed, similar to a battery. Each of theassembled component parts of the power generator 10 may further beenclosed in a suitable hollow structure such as a tube formed from asuitable material, such as polyethylene terephthalate (not shown), whichenclosure may also be capped on the top and/or bottom surfaces with asuitable cap (not shown), which cap may be removable and may be formedof a similar or different material as the enclosure. The power generator10 also may include at least one electrical connector through which adevice may be electrically connected to the power generator 10. Asillustrated in FIG. 1, in an embodiment of the invention, a device 52(schematically represented, not drawn to scale) may be electricallyconnected to the power generator 10 through electrical connectors 54 and56, which electrical connectors 54 and 56 may be connected to thecathode(s) and anode(s) of the fuel cell(s).

Electrical connectors 54 and 56 are also illustrated in FIG. 7. Inembodiments incorporating a plurality of fuel cells, the plurality offuel cells may be connected in series, and may be connected to a singleset of electrical connectors 54 and 56 protruding from the generatorhousing 36. In one embodiment of the invention, the power generator 10includes eight interconnected fuel cells.

Each of the parts of the power generator 10 and the valve 26 may befabricated of a suitable polymeric material, a metal or other materialas determined by the requirements of the intended use of the generatorand valve. One example material non-exclusively includes polyethyleneterephthalate. Dimensions of the component parts of the power generator10 may be very small in scale, but may also vary with respect to the useof the power generator 10. Outer dimensions of such a waterless,micro-power generator are from about 1 mm to about 100 mm in length,from about 1 mm to about 100 mm in width, and from about 1 to about 100mm in depth, or in a further embodiment, from about 1 mm to about 25 mmin length, from about 1 mm to about 25 mm in width, and from about 1 toabout 25 mm in depth. Such a waterless, micro-power generator is capableof incorporating one or more fuel cells 14 which fuel cells may range insize from about 0.1 mm² to about 5,000 mm². A waterless, micro-powergenerator of the invention may also be capable of containing a volumecapacity of from about 0.1 mm³ to about 15,625 cm³. A larger powergenerator may have dimensions of up to at least about 50 cm or more inlength, width and depth, up to at least about 5000 cm² or more in fuelcell area and up to at least about 0.125 m³ or more in power generatorvolume. While these dimensions are used in one embodiment, they may varywidely and are not intended to be limiting. The dimensions of each ofthe component parts of the power generator may similarly vary as couldbe determined by one skilled in the art in such a manner that the powergenerator of the invention will operate as intended.

In FIG. 7, channels 710, 712, 714, 716, and 718 to each of the fuelcells provide access to ambient. A rotatable ring 725 or multi-openinggate valve having corresponding openings 730, 732, 734, 736, and 738provide a shutoff valve function, such as a to each of the fuel cells byrotating the ring 725 with respect to the channels such that theopenings and channels do not line up, as shown in FIG. 7. Rotating thering 725 to line up the openings and channels provide access of the fuelcells to ambient, to provide additional water, such as in the form ofwater vapor to allow the fuel cells to resume producing electricity.

FIG. 8 is a cross section of an alternative power generator 800, havinga hydrogen producing fuel 810 and a proton exchange membrane based fuelcell 820 that is controllably exposed to ambient and hydrogen producedby the fuel 810. Fuel cell 820 may comprise one or more fuel cells inone or more layers in various embodiments. In one embodiment, a pressureregulated valve is disposed between the hydrogen producing fuel 810 andthe fuel cell 820. The valve consists of a pressure responsive flexiblediaphragm 825 disposed on a first side of the hydrogen producing fuel,and a piston or stem 830 connecting a valve plate 835 for seating on aplate 840. Plate 840 may be coupled to a power generator container 845and have an annular seat ring 850 for making a sealing contact with thevalve plate 835

In a further embodiment, a slide valve 855 or other type of valve iscoupled between the fuel cell 820 and ambient. An actuator such as aslide valve actuator 860 is coupled to the slide valve 855 for movingthe valve between an open position, allowing oxygen from ambient air ora controlled source to reach the fuel cell 820 and a closed position,which substantially if not fully prevents oxygen from reaching the fuelcell 820.

In one embodiment, the diaphragm 825 is designed with a spring constantsufficient to create a desired pressure of hydrogen between the fuel andthe plate valve 840. The valve regulates water vapor diffusion betweenthe fuel cells and the fuel. The spring constant of the valve thusdetermines the pressure difference between the inside of the powergenerator and the environment, also referred to as ambient.

It should be further understood that while several embodimentsillustrating various structures have been described, such structures arenot intended to be limiting. Other design variations that perform in asubstantially similar manner, i.e. waterless power generators capable ofproducing useful levels of electricity with hydrogen-oxygen fuel cellsincluding a solid fuel substance, are incorporated within the scope ofthe invention.

The Abstract is provided to comply with 37 C.F.R. §1.72(b) to allow thereader to quickly ascertain the nature and gist of the technicaldisclosure. The Abstract is submitted with the understanding that itwill not be used to interpret or limit the scope or meaning of theclaims.

1. A power generator comprising: a hydrogen producing fuel; a fuel cellhaving a cathode, proton exchange member, and an anode positionedbetween the fuel and ambient; a pressure regulated valve disposed at acavity extending from a membrane bordering the hydrogen producing fuelto the fuel cell, the pressure regulated valve to regulate exposure ofthe hydrogen producing fuel to water vapor from the fuel cell whenpressure between the hydrogen producing fuel and fuel cell is below apredetermined level; and a second valve positioned, in a single passageconfigured for both inlet and outlet, between ambient and the cathode ofthe fuel cell, wherein a geometry of the single passage is proportionedto deter diffusive water loss and thereby form a water retention zone atthe cathode of the fuel cell.
 2. The power generator of claim 1 whereinthe pressure regulated valve is coupled to a pressure responsiveflexible diaphragm.
 3. The power generator of claim 2 wherein thepressure regulated valve is coupled to a seat when pressure between thehydrogen producing fuel and fuel cell is above a predetermined level. 4.The power generator of claim 3 wherein the pressure regulated valveallows exposure of the hydrogen producing fuel to the fuel cell whenpressure between the hydrogen producing fuel and fuel cell is below apredetermined level.
 5. The power generator of claim 1 wherein thesecond valve is positioned between ambient and the fuel cell toselectively block a cathode of the fuel cell from ambient.
 6. The powergenerator of claim 5 wherein the second valve comprises a gate valve,butterfly valve, or ball valve.
 7. The power generator of claim 1wherein the fuel cell comprises multiple fuel cells arranged in a ring,and wherein the second valve comprises a multi-opening gate valve. 8.The power generator of claim 7 wherein the multi-opening gate valve thatis rotated to selectively expose or block the cathode to or fromambient.